1. Field of the Invention
This invention relates to a shearer loader for use in underground mining operations in which the shearer loader includes shearing drums connected through drive transmissions to a driving motor and a haulage box having a haulage box drive wheel connected by a reducing transmission to a driving motor for propelling the shearer loader along a mine face by engagement of a driving wheel of the haulage box with a rack or chain. The driving motor for the haulage box drive wheel is separate and independent from the driving motor for the shearing drums.
2. Description of the Prior Art
As disclosed in West German patent publication No. 1,171,376, it is known in the art to use a differential transmission in a mining tunneling machine to provide automatic control for the rate of advancement and a rate of cutting. The differential transmission is disposed in the shearing or cutting head of the mining machine. The machine drive motor supplies drive torque to the shearing drum by the differential transmission. The transmission takes the form of planetary gear transmission having a sun wheel connected by drive gears to the machine drive motor. The planetary gear transmission is also connected by drive gears to a hydraulic motor which drives the annulus of the planetary gear transmission and thereby supplies additional rotation to the transmission. The speed of the hydraulic motor can be varied in a stepless fashion and the direction of rotation can be reversed. In this motor and transmission arrangement, the speed of rotation provided by the machine drive motor can be adjusted in a stepless fashion by controlling the direction of rotation or by the output speed of the hydraulic motor whereby the output speed of the differential transmission is increased or reduced in a stepless fashion so that the shearing drum can be driven at a desired optimum speed.
Haulage boxes for shearer loaders used in underground mining are designed with a performance capability to operate at a maximum pull at a required rate of advancement of the mining machine. When the rate of advancement by the shearer loader overshoots a predetermined value, the maximum pull of the haulage box decreases because the product of the rate of advancement and pull is constant which determines the instantaneous output of the haulage box under any working condition.
Situations arise in underground mining operations that make it possible and even necessary for a shearer loader to be operated at a considerably greater rate of advancement if the haulage box could provide maximum pull at the increased rate of advancement. This is particularly true when fairly soft and free working coal seams are cut or when the operator of the shearer loader requires an extremely high mining performance beyond the driving power which the haulage box can provide.